Variable-output radiofrequency ablation power supply

ABSTRACT

A medical system is provided, including an ablation system having at least one ablation element and a sensor, a generator operable to deliver radiofrequency ablation energy to the ablation element. A power supply defines a duty cycle and provides a voltage to the generator, and the power supply has a duty cycle modulator and an amplitude modulator. A processor is connected to the power supply, the generator, and the sensor. The processor obtains a feedback signal from the sensor, and adjusts the duty cycle modulator and the amplitude modulator according to the feedback signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of and claims the benefit of U.S.patent application Ser. No. 12/716,893, filed Mar. 3, 2010, now U.S. PatNo. 8,556,891, the disclosures of which are herein incorporated byreference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates generally to medical systems and methodsof use thereof, and more particularly to an ablation system having avariable output power supply.

BACKGROUND OF THE INVENTION

Numerous procedures involving catheters and other minimally invasivedevices may be performed for a wide variety of treatments, such asablation, angioplasty, dilation or other similar therapies. For example,there are many variations of cardiac arrhythmias with different causes,including atrial fibrillation, generally involving irregularities in thetransmission of electrical impulses through the heart. To treat cardiacarrhythmias or irregular heartbeats, physicians often employ specializedablation catheters to gain access to interior regions of a patient'sbody. Such catheters include tip electrodes or other ablating elementsto create ablation lesions that physiologically alter the ablated tissuewithout removal thereof, disrupting or blocking electrical pathwaysthrough the targeted tissue. In the treatment of cardiac arrhythmias, aspecific area of cardiac tissue, such as for example atrial rotors,having aberrant electrically conductive pathways with erratic electricalimpulses is initially localized. A medical practitioner (such as aphysician) may direct a catheter through a body passage including forexample a blood vessel into the interior region of the heart that is tobe treated. Subsequently, the ablating portion of the selected device isplaced near the targeted cardiac tissue to be ablated, such as Forexample a pulmonary vein ostium or atrium.

An ablation procedure may involve creating one or more lesions in orderto electrically isolate tissue believed to be the source of anarrhythmia. During the course of such a procedure, a physician mayperform, for example, radio-frequency (RF) ablation which includesdiagnosing aberrant tissue and destroying it with local administrationof radio frequency energy. RF ablation may be performed by provide an RFelectrical signal to one or more electrodes in contact with the tissueto be ablated, and the energy resistively heats the surrounding tissue.Eventually, the heating process destroys the selected cells surroundingthe electrodes, and the ablation is completed.

Local conditions near the selected ablation site may change duringdelivery of RF ablation energy, for example due to fluid flow of bloodand possibly saline solution. These fluids may be electricallyconductive, and local fluid flow during ablation energy delivery to theelectrodes may alter the electrodes' impedance. Depending upon thespecific configuration of the medical system, the patient's anatomy andfluids near the ablation electrodes, the impedance characteristicsduring an ablation procedure may change by an amount ranging from afraction of an ohm to more than 200 ohms.

This significant variation in local conditions may lead to consequencessuch as for example some undesirable tissue ablation, local generationof steam, or other overheating. Given variations in anatomy and thepossibility of concurrent changes in the tissue treatment environmentand the potential effect such variation may have on a therapeuticprocedure, if is therefore desirable to provide a safe and effectivemedical ablation system having a feedback mechanism which automaticallyand continuously adjusts the ablation energy to ablate the desiredtissue to be treated. It is also desirable to provide an ablation systemand method for controlling the surface area and depth of ablation, andwhich automatically discontinues ablation once the desired treatment hasbeen achieved.

SUMMARY OF THE INVENTION

The present invention advantageously provides a medical system fortreating patients by ablating preselected tissue through the use of agenerator, a catheter with at least one ablation element, a patientreturn electrode, and a feedback system to verify and monitor theelectrical connection between the generator and the patient returnelectrode, as well as contact of the patient return electrode with thepatient.

In particular, a medical system is provided, including a catheter havingam ablation element and a sensor; a generator connected to the catheter,the generator being operable to deliver radiofrequency ablation energyto the ablation element; a power supply defining a duty cycle andproviding a voltage to the generator, the power supply having a dutycycle modulator and an amplitude modulator; and a processor connected tothe power supply, the generator, and the sensor; where the processor isoperable to obtain a feedback signal from the sensor, and adjust theduty cycle modulator and the amplitude modulator according to thefeedback signal.

A medical system is also provided, including a catheter having anablation element and a sensor; a generator connected to the catheter,the generator being operable to deliver radiofrequency ablation energyto the ablation element; a power supply defining a duty cycle andproviding a voltage to the generator; a proportional-integral-derivativecontroller operable to modulate the duty cycle; a variable resistancearray of parallel resistors connected to the sensor, and a switchconnected to each resistor; the variable resistance array being operableto modulate an amplitude of the voltage; a processor connected to thepower supply, the generator, and the variable resistance array; wherethe processor is operable to obtain a feedback signal from the sensor,and adjust the duty cycle and the amplitude according to the feedbacksignal

A method of treating a patient is provided, including providing anablation system having a power supply, a generator, an ablation element,and a sensor; determining a desired parameter value; operating the powersupply to define a duty cycle and an output voltage; placing theablation element and sensor proximate to a treatment site; deliveringelectrical power from the power supply to the generator, deliveringablation energy from the generator to the ablation element; measuring aparameter with the sensor; comparing the measured parameter to thedesired parameter value to determine a comparison value; and modulatingthe duty cycle and the output voltage to minimize the comparison value.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings, wherein:

FIG. 1 is an illustration of a medical system in accordance with theprinciples of the present invention;

FIG. 2 is an illustration of a circuit diagram for a variable-outputpower supply for the medical system of FIG. 1, in accordance with theprinciples of the present invention;

FIG. 3 is an illustration of a circuit diagram for a variable-outputpower supply having additional components in accordance with theprinciples of the present invention;

FIG. 4 is an illustration of a circuit diagram for a variable-outputpower supply having additional components in accordance with theprinciples of the present invention;

FIG. 5 is an illustration of a medical device in accordance with theprinciples of the present invention;

FIG. 6 is an illustration of the treatment assembly of FIG. 5, inaccordance with the principles of the present invention;

FIG. 7 is an illustration of another medical device in accordance withthe principles of the present invention;

FIG. 8 is a perspective illustration of a treatment assembly for themedical device of FIG. 7, in accordance with the principles of thepresent invention;

FIG. 9 is an illustration of the treatment assembly of FIG. 8, inaccordance with the principles of the present invention;

FIG. 10 is an illustration of another treatment assembly in accordancewith the principles of the present invention;

FIG. 11 is an illustration of an additional treatment assembly inaccordance with the principles of the present invention; and

FIG. 12 is an illustration of a flow diagram in accordance with theprinciples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention advantageously provides a medical system andmethod far treating patients by performing an ablation procedure inwhich a feedback mechanism can automatically and continuously adjust theablation energy to safely and effectively ablate the desired tissue tobe treated. In particular and as shown in FIG. 1, an ablation therapysystem, generally designated at 10, is provided for treating unwantedtissue conditions, including for example atrial fibrillation or otherarrhythmias. The ablation therapy system 10 may generally include apower supply 12 operably coupled to an electrical generator such as forexample a radio-frequency (“RF”) generator 14, an electrocardiogram.(“ECG”) unit 16 operably coupled to the RF generator 14, and a medicaldevice 18.

The medical device 18 may include a catheter for performing variousmedical treatments, including for example an electrophysiology catheterwhich may be operably coupled to the RF generator 14 and the ECG unit16. The medical device 18 may have a shape and dimensions to reachvarious treatments sites, such as intraluminal access to vascularanatomy, including for example transseptal access to the left atrium ofa patient's heart for subsequent treatment or ablation. The medicaldevice 18 may generally define an elongated, flexible catheter body 20having a distal treatment assembly 22, as well as a handle assembly 24at or near a proximal end of the catheter body 20.

The distal treatment assembly 22 may, for example, include one or moreablation elements such as electrodes 26 and one or more sensors such asthermocouples 28. Each electrode 26 may be electrically coupled to anoutput portion of the RF generator 14, and each thermocouple 28 may beelectrically coupled to a feedback portion of the RF generator 14. Ofcourse, the sensors may be of any suitable type, including for examplean electrical conductivity sensor, a spectrometer, a pressure sensor, afluid flow sensor, a pH sensor, and a thermal sensor.

Power supply 12 may accept an input voltage and produce an outputvoltage to the RF generator 14, which in turn delivers radiofrequencyablation energy to the ablation electrodes 26. The resulting thermalenergy at the electrodes 26 may then be verified and continuouslymonitored by the thermocouples 28, which send feedback signals back to aprocessor 30 which is connected to the power supply 12, the generator14, and the thermocouples 28.

A patient return electrode 32 may also be provided, and may include aconductive pad having a greater surface area than the electrodes 26. Thepatient return electrode 26 may be external to the patient, for examplein contact with the patient's skin through an adhesive attachment to theback of the patient, and may be operably coupled to the ECG unit 16and/or directly to the RF generator 14.

The ablation therapy system 10 may have one or more modes of operation,including for example: (i) bipolar ablation delivering ablation energybetween at least two of the electrodes 26 of the treatment assembly 22on the medical device 18 within a patient's body, (ii) monopolarablation delivering ablation energy to one of the electrodes 26 of thedistal treatment assembly 22 on the medical device 18 within a patient'sbody and through the patient return electrode 32 contacting a patient'sskin, and (iii) a combination of the monopolar and bipolar modes.

The RF generator 14 may also include a user interface 34 which mayinclude a display and/or a remote control 36, which enable a user toselect parameters for desired mapping and/or ablation treatment. Theuser interface 34 may allow the user to select an energy delivery modefor treatment, such as for example, selection among the delivery of onlymonopolar energy, only bipolar energy, or a combination of the two. Whenin combination mode, the user interface 34 may also allow selection apower ratio of monopolar energy to bipolar energy, such as 1:1, 2:1, or4:1. The RF generator 14 may offer a set of specific energy ratios bydefault, such, that the user can select one of the established energyratios, and/or the user interface can allow the user to enter adifferent custom energy ratio. The user interface 34 may also allowchanging the energy mode when the catheter is changed, or when themedical device 18 is moved to a different location to ablate differenttissue.

The ECG unit 16 may also have an ECG monitoring unit or display 38 tomonitor and map signals detected by the electrodes 26 of the distaltreatment assembly 22 of the medical device 18. The RF generator 14 andthe ECG unit 16 may both be operably coupled to the medical device 18.The ECG unit 16 may be designed to electrically isolate itself and thedisplay 38 from the signals generated by the RF generator 14, which mayinclude isolation from large magnitude signals and electrical noise thatmay result from the RF generator 14.

Power supply 12 may be a switched-mode power supply with a buckconverter which defines a duty cycle, and may have feedback mechanismsto adjust the output voltage, including for example a duty cyclemodulator and an amplitude modulator. Depending on the mode of operationat the moment, the power supply 12 determines a desired parameter forlocal conditions near the ablation elements. This desired parameter mayfor example be a desired temperature, and may be called the “setpoint.”

The feedback mechanisms obtain feedback signals from sensors near theablation elements, compare the feedback signals to the setpoint, andcalculate the difference between the desired setpoint and the feedbacksignals, to arrive at a comparison value.

The duty cycle modulator feedback mechanism may be aproportional-integral-derivative (PID) controller 40 which uses aprocessor algorithm to minimise the comparison value by adjusting thepower supply duty cycle. The PID controller 40 may take the form of asubset of the circuitry of processor 30, or any other suitablearrangement, including for example a software subroutine or a separatecontroller unit. In operation, the PID controller 40 calculates aproportional term based on the current comparison value, an integralterm based on the sum of recent comparison values, and a derivativevalue term based on the rate at which the comparison value has changed.The power supply duty cycle is then modulated by the PID controller 40,to adjust the power supply output voltage to the RF generator 14 andcontrol the ablation.

FIG. 2 depicts a circuit diagram, of a variable-output power supply 12for use in a medical ablation system shown in FIG. 1. Power supply 12may include a buck convertor 42, having an input voltage 44 andproducing an output voltage 46 based on feedback signals from thesensors (such as thermocouples 28 for example), and then adjusting theduty cycle modulator and the amplitude modulator according to thefeedback signals. The buck converter 42 may incorporate a regulator orprocessor 48 in the form of an integrated circuit, such as for examplethe commercially available integrated circuit LTC 1775. The specificexample of a buck converter 42 performs a variable step-down conversionof a direct current (DC) input voltage to a DC output voltage. The inputvoltage 44 may be selected among a range of suitable amounts, such asfor example a voltage equal to or less than 20 volts DC, including amore specific example of approximately 4.7 volts. The processor 48 maybe combined with several components such as for example an inductor 50,a capacitor 52, a resistor 54, and a variable resistance 56.

FIG. 3 depicts a more specific example of a variable-output power supplyhaving a buck convertor 58 with a PID controller to modulate the dutycycle, in which the input voltage 44, the output voltage 46, theinductor 50, the capacitor 52, the resistor 54, and the variableresistance 56 are indicated by the same reference numerals as those inFIG. 2. A regulator or processor 60 is more complex than the processor48 of FIG. 2, and additional components are added including for examplean additional resistor 62, a diode 64, and capacitors 66. Additionalresistor 62 may for example serve to raise the input voltage to theprocessor 60 greater than input voltage 44, which may improve overallefficiency of the power source. Diode 64 may be a conventional diode, oras a more specific example may be a Schottky diode, and may operate torecharge a capacitor which powers a field effect transistor (FET) insidevariable resistance 56. Capacitors 66 may assist in handlingroot-mean-square (RMS) current at the input, and avoiding ripple at theoutput 46.

FIG. 4 shows a variable-output power supply 68 with even more detail,and which adds a variable resistance array for amplitude modulation. Forexample, processor 70 accepts an input voltage 72 and produces an outputvoltage 74, based on feedback signals from the sensors for examplethermocouples 28, and then adjusts the duty cycle modulator as well asthe amplitude modulator according to the feedback signals. Inparticular, an inductor 76, a capacitor 78, and a resistor 80 perform ina similar manner as those in FIG. 2, and circuit includes additional,components such as for example resistors 82, diodes 84, capacitors 86,and transistors 88. These additional components may be selected to havea variety of suitable characteristics. More specifically, the specifictype of transistors may be metal-oxide semiconductor field-effecttransistors.

The amplitude modulator feedback mechanism may be a variable resistancearray 90, operably coupled between the processor 70 and thethermocouples 28. The variable resistance array 90 has a plurality ofparallel resistors 92A-H, each of which is coupled with a FET thatcombines the features of a diode 94A-H and a transistor 96A-H. Based onthe feedback signals from the thermocouples 28, the processor 30 mayactivate one of the transistors 96 to allow current to flow through thecorresponding resistor 94 and thus modulate the amplitude of the dutycycle.

In the specific example shown in FIG. 4, eight parallel resistors 92A-Hare illustrated, though any suitable number of parallel resistors may beselected. Also, each parallel resistor 92 may be selected to have adifferent resistance, and in a specific example they may have thefollowing sequence of resistances in ohms: 1024 k, 512 k, 256 k, 128 k,64 k, 32 k, 16 k, and 8 k. Of course, any suitable variety of parallelresistances may be chosen.

Now referring to FIGS. 5-11, some exemplary medical devices aredepicted. In particular, FIG. 5 shows an ablation catheter 100 having adistal treatment assembly 102 in which the electrodes 26 have a linearconfiguration. The distal treatment assembly 102 may be used for bipolarablation between the electrodes 26 of the distal treatment assembly 102,or for monopolar ablation, between one electrode 26 and a patient returnelectrode 32, or a combination of bipolar ablation and monopolarablation. A proximal handle 104 has a rotational actuator 106 formanipulating, bending, steering and/or reshaping the distal treatmentassembly 102 into various desired shapes, curves, etc. FIG. 6 shows thedistal treatment assembly 102 in greater detail, including theelectrodes 26 and the thermocouples 28.

FIGS. 7-9 show an ablation catheter 108 with a distal treatment assembly110 in which the electrodes have a planar configuration. Similar to theablation catheter 100, the distal treatment assembly 110 may be used forbipolar ablation, monopolar ablation, or a combination thereof. Aproximal handle 112 has a rotational actuator 114 for manipulating adistal portion of the ablation catheter 108, and a linear actuator 116.The linear actuator 116 can advance the distal treatment assembly 110distally beyond a catheter shaft, and retract the distal treatmentassembly 110 proximally inside the catheter shaft. When the distaltreatment assembly 110 is advanced distally, it may resiliently expandfrom a compressed arrangement inside the catheter shaft to the deployedarrangement shown in FIGS. 8 and 9.

FIG. 10 shows a catheter 118 which has a distal treatment assembly 120having a resilient framework in which the electrodes have aproximally-directed configuration, which may for example be used fortransseptal treatments of a patient's heart.

FIG. 11 shows a catheter 122 which has a distal treatment assembly 124in which the electrodes have an adjustable linear, planar, or spiralconfiguration.

Accordingly, the medical, device 18 may be used to investigate and treataberrant electrical impulses or signals in a selected tissue region,such as in the heart. Primarily, the distal treatment assembly 22 may beadvanced through the patient's vasculature via the femoral artery over apreviously inserted guidewire. The distal treatment assembly 22 may thenbe advanced into the right atrium and into proximity of a pulmonaryvein, for example.

In an exemplary use of the present system, as illustrated in the flowdiagram of FIG. 12, the medical system is first prepared for ablation,and the ablation system is set up (step 200). One or more patient returnelectrodes are placed (step 202), and the ablation catheter is placed sothat a distal treatment assembly having electrodes and sensors is in thedesired position for treatment (step 204). Various ablation parametersare determined, including the intended duration of ablation (step 206).The desired ablation mode is selected, for example monopolar ablation,bipolar ablation, or a specific combination thereof, and the expectedfeedback parameter value is determined (step 208). For example, if thesensors are thermal sensors, then an expected feedback parameter valuemay be selected at a temperature which is below a fluid boilingtemperature under local conditions, which may be 100 degrees Celsius.

If all parameters are not acceptable (step 210), then the setup andparameters are evaluated and corrected (step 212). If all parameters areacceptable, then delivery of ablation energy may commence. A powersupply is operated, defining a duty cycle providing an output voltage toa generator (step 214), and ablation energy is delivered from thegenerator to the electrodes (step 216).

During ablation, a feedback parameter is continuously measured (step218), and the measured feedback parameter is compared, to the expectedfeedback parameter to determine a comparison value (step 220). The dutycycle and amplitude are independently modulated to minimize thecomparison value (step 222). When ablation is complete (step 224), theablation system stops delivering energy (step 224).

While examples and illustrations of particular medical systemconfigurations have been provided, it is understood that variousarrangements, shapes, configurations, and/or dimensions may be includedin the medical device of the present invention, including but notlimited to those illustrated and described herein. Also, thoughmonopolar and bipolar RF ablation energy may be the selected forms ofenergy to pass through the electrodes of the medical device, other formsof ablation energy may be additionally or alternatively emitted from thetreatment assembly, including electrical energy, magnetic energy,microwave energy, thermal energy (including heat and cryogenic energy)and combinations thereof. Moreover, other forms of energy that may beapplied can include acoustic energy, sound energy, chemical energy,photonic energy, mechanical energy, physical energy, radiation energyand a combination thereof.

It should be understood that an unlimited number of configurations forthe present invention could be realized. The foregoing discussiondescribes merely exemplary embodiments illustrating the principles ofthe present invention, the scope of which is recited in the followingclaims. In addition, unless otherwise stated, all of the accompanyingdrawings are not to scale. Those skilled in the art will readilyrecognize from the description, claims, and drawings that numerouschanges and modifications can be made without departing from the spiritand scope of the invention.

What is claimed is:
 1. A method of treating a patient with an ablationsystem having a generator, an ablation element, a sensor, and a powersupply comprising a variable resistance operatively coupled between thesensor and a processor, the method comprising: selecting an energydelivery mode for treatment from at least one of monopolar ablationenergy and bipolar ablation energy; selecting a desired value of anoperating parameter; placing the ablation element and sensor proximateto a treatment site; delivering an electrical output from the powersupply to the generator; delivering ablation energy from the generatorto the ablation element; measuring a value of the operating parameterwith the sensor; comparing the measured value of the operating parameterto the desired value of the operating parameter to determine acomparison value; and modulating the amplitude of the electrical outputfrom the power supply by the processor altering the variable resistancebased on the comparison value.
 2. The method of claim 1, wherein theoperating parameter is temperature.
 3. The method of claim 1, whereinthe variable resistance comprises a field-effect transistor (FET). 4.The method of claim 3, wherein the variable resistance further comprisesa resistor coupled with the FET.
 5. The method of claim 4, wherein theFET comprises the features of a diode and a transistor, and whereinaltering the variable resistance comprises the processor activating thetransistor to allow current to flow through the resistor.